Commit bd63141d authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

blk-mq: clear stale request in tags->rq[] before freeing one request pool 



refcount_inc_not_zero() in bt_tags_iter() still may read one freed
request.

Fix the issue by the following approach:

1) hold a per-tags spinlock when reading ->rqs[tag] and calling
refcount_inc_not_zero in bt_tags_iter()

2) clearing stale request referred via ->rqs[tag] before freeing
request pool, the per-tags spinlock is held for clearing stale
->rq[tag]

So after we cleared stale requests, bt_tags_iter() won't observe
freed request any more, also the clearing will wait for pending
request reference.

The idea of clearing ->rqs[] is borrowed from John Garry's previous
patch and one recent David's patch.

Tested-by: default avatarJohn Garry <john.garry@huawei.com>
Reviewed-by: default avatarDavid Jeffery <djeffery@redhat.com>
Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210511152236.763464-4-ming.lei@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 2e315dc0

block/blk-mq-tag.c

+7 −2
Original line number Original line Diff line number Diff line
@@ -202,10 +202,14 @@ struct bt_iter_data { 
static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,

static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,

		unsigned int bitnr)

		unsigned int bitnr)

{

{

	struct request *rq = tags->rqs[bitnr];

	struct request *rq;

	unsigned long flags;





	spin_lock_irqsave(&tags->lock, flags);

	rq = tags->rqs[bitnr];

	if (!rq || !refcount_inc_not_zero(&rq->ref))

	if (!rq || !refcount_inc_not_zero(&rq->ref))

		return NULL;

		rq = NULL;

	spin_unlock_irqrestore(&tags->lock, flags);

	return rq;

	return rq;

}

}
@@ -538,6 +542,7 @@ struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags, 




	tags->nr_tags = total_tags;

	tags->nr_tags = total_tags;

	tags->nr_reserved_tags = reserved_tags;

	tags->nr_reserved_tags = reserved_tags;

	spin_lock_init(&tags->lock);





	if (blk_mq_is_sbitmap_shared(flags))

	if (blk_mq_is_sbitmap_shared(flags))

		return tags;

		return tags;

block/blk-mq-tag.h

+6 −0
Original line number Original line Diff line number Diff line
@@ -20,6 +20,12 @@ struct blk_mq_tags { 
	struct request **rqs;

	struct request **rqs;

	struct request **static_rqs;

	struct request **static_rqs;

	struct list_head page_list;

	struct list_head page_list;



	/*

	 * used to clear request reference in rqs[] before freeing one

	 * request pool

	 */

	spinlock_t lock;

};

};





extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags,

extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags,

block/blk-mq.c

+41 −5
Original line number Original line Diff line number Diff line
@@ -2307,6 +2307,45 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio) 
	return BLK_QC_T_NONE;

	return BLK_QC_T_NONE;

}

}





static size_t order_to_size(unsigned int order)

{

	return (size_t)PAGE_SIZE << order;

}



/* called before freeing request pool in @tags */

static void blk_mq_clear_rq_mapping(struct blk_mq_tag_set *set,

		struct blk_mq_tags *tags, unsigned int hctx_idx)

{

	struct blk_mq_tags *drv_tags = set->tags[hctx_idx];

	struct page *page;

	unsigned long flags;



	list_for_each_entry(page, &tags->page_list, lru) {

		unsigned long start = (unsigned long)page_address(page);

		unsigned long end = start + order_to_size(page->private);

		int i;



		for (i = 0; i < set->queue_depth; i++) {

			struct request *rq = drv_tags->rqs[i];

			unsigned long rq_addr = (unsigned long)rq;



			if (rq_addr >= start && rq_addr < end) {

				WARN_ON_ONCE(refcount_read(&rq->ref) != 0);

				cmpxchg(&drv_tags->rqs[i], rq, NULL);

			}

		}

	}



	/*

	 * Wait until all pending iteration is done.

	 *

	 * Request reference is cleared and it is guaranteed to be observed

	 * after the ->lock is released.

	 */

	spin_lock_irqsave(&drv_tags->lock, flags);

	spin_unlock_irqrestore(&drv_tags->lock, flags);

}



void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,

void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,

		     unsigned int hctx_idx)

		     unsigned int hctx_idx)

{

{
@@ -2325,6 +2364,8 @@ void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, 
		}

		}

	}

	}





	blk_mq_clear_rq_mapping(set, tags, hctx_idx);



	while (!list_empty(&tags->page_list)) {

	while (!list_empty(&tags->page_list)) {

		page = list_first_entry(&tags->page_list, struct page, lru);

		page = list_first_entry(&tags->page_list, struct page, lru);

		list_del_init(&page->lru);

		list_del_init(&page->lru);
@@ -2384,11 +2425,6 @@ struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set, 
	return tags;

	return tags;

}

}





static size_t order_to_size(unsigned int order)

{

	return (size_t)PAGE_SIZE << order;

}



static int blk_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,

static int blk_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,

			       unsigned int hctx_idx, int node)

			       unsigned int hctx_idx, int node)

{

{